Modern high-performance computer processors and ASICs require high current at low voltage. A typical processor today may require anywhere from a 0.7 V to 1.1 V core voltage with peak currents exceeding 200 A. A DC-DC regulator placed close the processor minimizes the distance that the high current must travel through the circuit board from the regulator source to the processor load. Several DC-DC converters may be used in parallel, in order to deliver a higher total load current. Typical currents per converter are from 40 A to 60 A. Systems commonly use from one to eight converters in parallel.
The ubiquitous means of delivering power to the DC-DC converters is to distribute a 12 V intermediate bus within the system drawer or rack. The high currents involved in distributing 12 V can present challenges for systems that have high power or which distribute the intermediate bus over longer distances throughout a rack. The conductors that carry the 12 V intermediate bus dissipate power as the current squared times the resistance of the conductors. As power rises or current increases the losses increase as the square of the load current. To lower resistance more copper cross-section is needed, resulting in heavier cables, more connector pins, and more layers of copper in a printed circuit board (PCB).
A well-known solution to distributing intermediate bus power raises the voltage to decrease the current. The industry has established through agency regulation that voltages less than 60 V are considered safe and do not require that special provisions be made to shield people from having access to these circuits. In the industry, a 48 V intermediate bus is a widely adopted solution for telecom hardware systems and for some other systems having rack-level distribution of the intermediate bus. In some systems, a converter transforms the 48 V DC intermediate bus to 12 V DC, so that the traditional 12 V to processor voltage DC-DC converters can still be used. Thus, the system's overall DC-DC power conversion from 48 V to processor voltage consists of multiple power conversion stages in series. Each power conversion stage takes up physical space and consumes power.
Another option that has been adopted by some of the industry is to directly convert from a 48 V DC intermediate voltage to the sub 1 V processor voltage in a single conversion step stage. Such designs both eliminate the power loss, volume, and material cost of the separate 48 V to 12 V conversion stage and reduce the intermediate bus distribution losses, due to the 4× reduction in intermediate bus current.
Further, common 12 V to sub 1 V DC-DC converters do not have transformers and use switches or diodes to directly connect from the 12 V intermediate bus to the output inductor for part of the converter's switching cycle. For higher voltage intermediate busses in the range of 48 V, however, it becomes difficult to directly connect the output switching devices to the intermediate bus. The “on time” of the 48 V to inductor switch is short, the duty cycle is small and switch timing is difficult to control. Hence, many vendors are now designing 48 V to sub 1 V DC-DC converters that include transformers and have the switching secondary-side Field Effect Transistors (FETs) connected between the secondary side of the transformer and the output inductor. The transformer-based industry DC-DC converter designs to date have separate transformers and inductors. The magnetic ferrite cores for these transformers and inductors take up significant physical volume and make transformer-based DC-DC converters less space- and cost-efficient.